Tachyarrhythmias are episodes of high-rate cardiac depolarizations. Tachyarrhythmias may occur in one chamber of the heart or may be propagated from one chamber to another. Some tachyarrhythmias are sufficiently high in rate to compromise cardiac output from the chamber(s) affected, leading to loss consciousness or death, in the case of ventricular fibrillation or weakness and dizziness in the case of atrial fibrillation. Atrial fibrillation is often debilitating, due to the loss of atrial cardiac output, and may sometimes lead to ventricular fibrillation.
Generally, fibrillation may be terminated by administering high energy level cardioversion/defibrillation shocks or pulses until the fibrillation is terminated. For example, in the context of implantable anti-arrhythmia devices, these pulses may be applied by means of large surface area electrodes on or in the chamber to be defibrillated. However, the high energy level pulses are often sufficient to cause pain to the patient. Thus, it would be desirable to prevent or decrease the occurrence of atrial fibrillation without the delivery of high energy level pulses.
Some exploration has, therefore, been made in the use of pacing level pulses, which stimulate the cardiac tissue at much lower levels than defibrillation pulses, to terminate atrial fibrillation.
Implantable pulse generators (IPGs) that deliver pacing level pulses are well known in the art. These IPGs may deliver pulses to one or more chambers of the heart. Some of these devices provide pacing stimuli to the heart at a predetermined rate. The stimuli may be applied at a fixed rate, on demand, at a rate synchronized to atrial activity or at a rate synchronized to ventricular activity. This type of pacing function may also be used in other devices such as, for example, implantable cardioverter defibrillators (ICDs) or in external pacemakers. Most IPGs include sense amplifier circuitry for detecting intrinsic cardiac electrical activity. Some IPGs also include sensors or sensing electrodes to determine reliably the heart rate (or pacing rate) in a heart under different conditions. Some IPGs are dual-chamber, having both atrial and ventricular leads. These IPGs have a unipolar lead in the ventricle and a unipolar lead in the atrium.
To deliver pacing pulses of sufficient magnitude to have the desired effect, it may be desirable to stimulate or sense more than one chamber of the heart simultaneously. This may be desirable, for example, because the simultaneous stimulation in opposing chambers results in stimulation pulses of higher amplitude or duration. This may also be desirable because stimulation across opposing chambers of the heart stimulates a desired location of tissue that is more difficult to stimulate across only one chamber of the heart. In standard IPGs, a minimum atrio-ventricular delay makes such simultaneous stimulation difficult or impossible. That is, there is a minimum delay between the time a first chamber, for example the left atria, is stimulated/sensed and the time the second chamber, for example the right atria, is stimulated/sensed.
It would also be desirable to provide stimulation to opposing chambers of the heart using standard programming settings and existing fixed connections in an IPG without the addition of further splitters and adapters.
It would also be desirable to provide switchable configurations of electrodes disposed in opposing atria or ventricles of the heart.
Thus, a need exists in the medical arts for simultaneous stimulation and/or sensing of opposing chambers of a heart.
Several methods have been proposed in the prior art for improving an implantable device's ability to administer pacing pulses simultaneously to more than one chamber of a heart.
For example, U.S. Pat. No. 5,514,161 to Limousin, entitled “Methods and Apparatus for Controlling Atrial Stimulation in a Double Atrial Triple Chamber Cardiac Pacemaker”, hereby incorporated by reference in its entirety, discloses a double atrial triple chamber pacemaker, which provides simultaneous stimulation to both atria through the provision of a Y connector.
U.S. Pat. No. 5,757,970 to Pouvreau, entitled “System, Adaptor and Method to Provide Medical Electrical Stimulation” discloses an adaptor that permits a single channel of stimulation to be split and provided to two areas of the heart by adjusting the amplitude of the stimulation pulses.
The article “Permanent Multisite Cardiac Pacing” by Barold, et al. in the journal PACE discloses the use of a Y connector to split a standard bipolar output into anode and cathode electrodes.
The article “Hemodynamic Benefits of Permanent Atrial Resynchronization Patients with Advanced Inter Atrial Blocks, paced DDD Mode” by Daubert et al. in the journal PACE discloses the use of a bifurcated electrode to pace between the right atrium and the coronary sinus in order to pace both atria simultaneously.
As discussed above, the most pertinent prior art patents are shown in the following table:
TABLE 1Prior Art PublicationsU.S. Pat. No.DateInventor(s)U.S. Pat. No. 5,514,161May 7, 1996LimousinU.S. Pat. No. 5,757,970Aug. 25, 1998PouvreauBarold et al. (November 1997) “System, Adaptor and Method to Provide Medical Electrical Stimulation” PACE, Vol. 20, pages 2725-2729. Daubert et al. (April 1997) “Hemodynamic Benefits of Permanent Atrial Resychronization Patients with Advanced Inter Atrial Blocks, paced DDD Mode” PACE, Vol. 14, Part II, page 640, #130. 
All the publications listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.